Stripe already is a second place, non centralized, off platform.
I don't want to hunt down my predatory subscriptions in multiple places.
In the same vein: Games don’t cost less on the epic store despite their lower (compared to Steam) either, so as an end user it makes no difference where I buy games.
Maybe you like paying an extra 20%. That's your business. But fees like that affect the viability of lots of business ideas, including games. Having lower fees increases the pool of indie games.
You can't say a slave is free because their master is free to enslave them, and they're free to escape if they can. Sometimes you need rules to create real freedom.